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CHEMICAL :

CHEMICAL THERMODYNAMICS

Introduction :

Introduction Thermodynamics is the branch of science that deals with the study of inter conversion of heat with other forms of energy during physical and chemical processes.
It mainly deals with transformation of energy.
All physical and chemical processes are accompanied by the absorption liberation and conversion or redistribution of energy.

Objectives :

Objectives To predict flexibility of a process under a given set of conditions
To predict whether a reaction is spontaneous or not.
It is a state function and not a path function.i.e; it depends on initial and final states

Certain Terms :

Certain Terms System-is a specified portion of universe which is under thermodynamic study and is separated from the universe with a definite boundary. Eg- the earth is a system .
Surroundings- is the portion of the universe excluding the system which is capable of exchanging energy and matter with the system eg:- the entire universe excluding the earth forms the earth`s surrounding .
Boundary- the real or imaginary surface that separates the system from the surrounding . Eg:- the atmosphere can be considered as earth`s boundary from the universe.

Types of Systems :

Types of Systems There are three types of systems
Open System
Closed System
Isolated system

Open System :

Open System An open system is a system which can exchange both matter and energy with the surrounding. Eg:-water in an open beaker is an open system as it can exchange both energy and matter with the surrounding.

Closed System :

Closed System A closed system is one which can exchange energy but not matter with the surroundings.
Eg:- Hot water in contact with its vapour in a closed container.

Isolated System :

Isolated System An isolated system is a system which can neither exchange matter nor energy with the surroundings.
Eg:- Water in contact with its vapour in a closed insulated vessel is an isolated system.

State of a system :

State of a system The state of a system is the condition of the system expressed by giving definite values for its properties such as temperature , pressure , volume etc.
State function : The variables like temperature , pressure , volumes .etc. which define the state of a system are called state functions or thermodynamic variables .
The values of state function depend only on the state of the system and not upon the way in which the state is reached .
Work and heat are not state functions .

Thermodynamic Processes :

Thermodynamic Processes A process is an operation which brings about changes in the state of a system. It is accompanied by the changes in energy and mass .
Standard state :- The state of a system at 298K and 101.3 kPa pressure is known as standard state of a system .

Types of Processes :

Isothermal Process :

Isothermal Process Isothermal process is a process during which the temperature of a system is constant .
It is a process carried out in a closed vessel .
For an isothermal process , dT=0 .
Eg :- the melting and solidification of wax at the same temperature is an isothermal process .

Adiabatic Process :

Adiabatic Process Adiabatic process is a process during which no heat is exchanged between the surrounding and the system .
Adiabatic process is carried out in an isolated vessel .
For an a adiabatic process , dq=0 .
Eg :- Bursting of a high pressure tyre tube is close enough to an adiabatic process .

Isobaric Process :

Isobaric Process It is a process during which the pressure remains constant .
They are carried out in an open process .
For an isobaric process , dP=0 .
Eg :- A chemical reaction carried out in a test tube .

Isochoric Process :

Isochoric Process It is a process where volume remains constant .
It is carried out in a closed vessel .
For an isochoric process , dV=0 .

Reversible Process :

Reversible Process A process which can be reversed at any instant of time by increasing the opposing force by an infinitesimally small amount .
It is a process carried out at a very small rate .
Eg :- Compression and expansion of a gas by a piston in an isolated vessel at an infinitesimally small rate .

Irreversible Process :

Irreversible Process It is a process which is carried out rapidly so that the system does not get a chance to attain equilibrium .
All spontaneous processes occuring in nature are irreversible .
It cannot be reversed at any stage .
Eg :- Burning of paper .

Cyclic Process :

Cyclic Process A process during which the system undergoes a series of changes and returns to its initial state .
Eg :- Water cycle , Carbondioxide cycle .

Properties of the System :

Properties of the System Intensive property of a system is a property of a system which does not depend on the quantity of substance present in the system. For example : density , viscocity , surface tension , pressure, temperature and many more…..
Extensive property of a system is a system which depends upon the quantity of substance present in the system .for example mass , volume , energy ,enthalpy and many more……..

Internal Energy (U) :

Internal Energy (U) Internal energy is the energy possessed by the system due to its nature chemical composition and thermodynamic state .
Its value depends on the mass of the system and its state .
It is made up of a number of energies like kinetic , nuclear , translational and many more .
It is an extensive property.
Its definite vale cannot be determined but change in internal energy can .
It is directly proportional to the temperature of the system

Laws of Thermodynamics :

Laws of Thermodynamics There are four laws of thermodynamics namely :
First law of thermodynamics
Second law of thermodynamics
Third law of thermodynamics
Zeroth law of thermodynamics

First law of thermodynamics :

First law of thermodynamics First law of thermodynamics states that energy lost in one form results in energy reappearing in another form . It means the energy of a system is constant .
Mathematical form of the law is
dU=q+W.,where dU is change in internal energy , q is heat energy and W is work done on the system .

Sign convention :

Sign convention The following are the sign convention used according to IUPAC
heat absorbed by system ,q is +ve
Heat evolved by the system ,q is –ve
Work done on the system , w is +ve
Work done by the system , w is -ve

Work done in an isothermal process :

Work done in an isothermal process When an ideal gas undergoes compression or rarefaction , temperature of system is constant therefore internal energy is zero
dU = q+W
0=q+w
w=-q
Hence the mechanical work done during isothermal change is equal to thwe quantity of heat absorbed or evolved by the system.Mechanical work done in an isothermal process for an ideal gas is given by
W=-2.303 nRT log V2/V1(or P1/P2)for n moles of gas .

Mechanical work done during Adiabatic Process :

Mechanical work done during Adiabatic Process During this process no heat is exchanged with t he surroundings therefore q=0.
According to first law of thermodynamics
dU =q +W
dU= 0 +W
dU= W
hence work done in expense of internal energy
For an ideal gas the adiabatic work done is given by
W= nCv ( t2-t1) for n moles of gas
Where Cv is molar heat capacity at constant volume ,t2 and t1 are final and initial temperatures respectively.